The forward, who has scored 10 goals in the Championship this term, has penned a three-and-a-half year deal with Owen Coyle's side
The 20-year-old penned a three-and-a-half year deal on deadline day and becomes the third player to arrive at the Reebok in the January transfer window following Tim Ream from New York Red Bulls and Ryo Miyaichi, who signed on a loan deal from Arsenal until the end of the season.
Sordell has netted 10 times in the Championship for Watford this season and has made six appearances for England's Under-21 side.
"I am delighted to have brought Marvin to our club, as there were a number of other Premier League clubs tracking him," Coyle told the club's official website.
"We know that he has great potential and I am really looking forward to working with him.
"Overall, we're very pleased with all the players we have been able to bring in, as we have strengthened and added real quality signings to our squad."
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